Recently Flat Panel Displays (FPDs) have become popular due to their smaller footprint and larger flatter screen compared to conventional technology. Liquid Crystal Displays (LCD) are replacing Cathode Ray Tubes (CRT) in many domestic applications. However, most LCDs have the disadvantage of a low contrast ratio (5000:1) compared to conventional CRT technology (1,000,000:1). To improve the contrast ratio of an LCD, multi-segment operation of a backlight is being studied actively by many researchers. Multi-segment operation is a method in which a segment of the display which is located in a bright portion of the picture is illuminated more brightly and other segments which are located in darker portions of the picture are less illuminated. The intensity of each segment is controlled according to the displayed picture. The smaller the size of the segments the better the fidelity of the display. Light Emitting Diodes (LED) are usually used as the light sources of a multi-segment operated backlight. For example, it is known for 400 LEDs to be aligned in a 20×20 matrix on the backlight panel. This LED array is divided into 25 segments so that each segment has 16 (=4×4) LEDs. The image which is supposed to be displayed by the LCD panel is analysed in advance and the intensity of each segment is determined so as to maximize the contrast ratio of displayed picture. The LED backlight usually creates a white light from 3 kinds of LEDs, namely Red, Blue and Green, so it is difficult to make the size of the segment too small. If the area of a segment is too small, appropriate white light cannot be obtained because 3 colours are not mixed well.
An alternative technology to LCD is a Field Emission Display (FED). A typical FED incorporates a large array of fine metal tips or carbon nano-tubes (CNT), which emit electrons through a process known as field emission. Since a FED works based on a similar principle to a CRT, namely using an electron emitter and a phosphor, it gives a sufficiently high contrast ratio. However, the fabrication of so-called Spindt-type emitters, which are utilized for most FED systems, requires complex processes and increases the cost of the panel. Synthesis of CNT is also costly because it requires expensive equipment. These are the major reasons why FED cannot play a main role in the FPD industry in spite of its potential to achieve a high contrast ratio.
It would therefore be desirable to provide a backlight for LCD which has a lot of small segments which can each be operated independently, or an electron emitter array for a FED which enables low production cost.